ABSTRACT
Meso-nitrile oxide group in 1,7-Diphenyl-containing BODIPYs can be involved in highly unusual [3+2] intramolecular cycloaddition reaction with the formation of the dihydrobenzo[d]isoxazole-containing BODIPYs. Oxidation of these compounds results in the formation of unprecedented either benzisoxazole- or benzo[b]azepine-fused fully conjugated NIR absorbing BODIPYs. The photophysical properties and electronic structures of the target compounds were studied by an array of experimental and theoretical methods.
ABSTRACT
We report here one of the rare examples of expanded hexaphyrins named as dithia pyribenzihexaphyrin macrocycles containing six-membered rings such as pyridine and p-phenylene along with five-membered heterocycles such as pyrrole and thiophene as a part of a macrocyclic frame. Trifluoroacetic acid catalyzed [3 + 3] condensation of equimolar mixture of [10,10'-bis(p-tert-butyl phenyl)hydroxymethyl]-1,3-bis(2-thienyl)pyridine diol (2,6-pyri diol) and 1,4-bis(phenyl(1H-pyrrol-2-yl)methyl)benzene (p-benzidipyrrane) in CH2Cl2 followed by oxidation with DDQ afforded stable nonaromatic dithia 2,6-pyri-para-benzihexapyrins 1 and 2 in 6-8% yields. The macrocycles were characterized by high-resolution mass spectroscopy and 1D and 2D NMR spectroscopy. NMR studies revealed the nonaromatic nature of dithia 2,6-pyri-p-benzihexaphyrins and indicated that the para-phenylene ring prefers to be in quininoid form rather than in benzenoid form. The macrocycles displayed sharp absorption bands in the region of â¼380-500 nm and a broad band at â¼700 nm, reflecting their nonaromatic nature. Upon protonation, these macrocycles showed NIR absorption properties. The redox studies of macrocycles indicated their electron-deficient nature. The DFT/TD-DFT studies are in line with the experimental observations.